This story in EDN provides more insights about the situation in P1901:

http://www.edn.com/blog/630000263/post/220026822.html

The [...] proposal selected by the IEEE P1901 WG on October 2007 is very peculiar and will likely look strange to any engineer familiar with IEEE standards. The document is the perfect example of how not to write a specification: it includes two completely incompatible specifications for the specification“Physical Layer” (PHY) and for the “Data Link Layer”. One of the specifications is based on OFDM modulation while the other is based on Wavelet modulation. Vendors are not required to implement both options (and I predict that nobody will). The modulation schemes are mutually incompatible, so IEEE P1901 products based on OFDM modulation will not interoperate with products based on Wavelet modulation.

Let me repeat that again, just in case you have not fully understood the implications: "IEEE P1901 products based on OFDM modulation will not interoperate with products based on Wavelet modulation".

[...]